1887] -~ Mineralogy and enaA 569 
deposits of this region were also examined. This ore is com- 
posed essentially of ocililedrát crystals of magnetite imbedded 
ark green mineral with the Caton AE and optical char- 
De si hercynite (or pleonaste, with a very low percentage 
of magnesium). This mineral is also found disseminated in small 
Ue ahedral crystals in the rock adjoining the ore veins. Associ- 
ated with the magnetite and hercynite of the ore occur also 
fibrolite and corundum. 
garded merely as an altered peridotite. The remains of bronzite 
crystals can still be detected in the rock, and consequently the 
view of Professor Sterry Hunt, that it must be looked upon as 
an altered sediment because of its intimate association with sed- 
imentary beds of gypsum, can no longer be maintained. Ina 
preliminary “ Note on the Volcanic and Rseitinted Rocks of the 
‘Neighborhood of Nuneaton,” England, T. H. Waller? mentions 
the occurrence there of ashes (tufa) composed of pieces of feld- 
spar, a little quartz, and grains of some basic rock; a felsite with 
‘porphyritic crystals of quartz, in which lines of secondary fluid 
inclusions are well exhibited ; a diabase porphyrite with augite 
twinned according to both twinning laws,—viz., parallel to oP 
and «Px ; and, finally, indurated quartzites with the individual 
quartz grains enlarged by the addition of new quartz material | 
whose optica = orientation is identical with that of the original 
ins. connection with the statement of Dr. Williams in 
regard to he seepentine of Syracuse, it may be of interest to call 
attention to an article in which J. H. Tee cites several exam- 
ples to prove that “some beds of a common series have been 
changed into serpentine, while others fesse over) sig poera 
schist.” He thinks that many of the serpentines of Cornwall, 
which have heretofore been regarded as having eena by the 
alteration of intrusive sheets of picrite, may as well be considered 
as having originated in some other manner. 
r. Jo ur. Science, xx., 1880, p. 218. 
. i Galena, March, 1887, p 232. 
3 Geological Magazine, Jay, 1886, p- 322. 
4 Ib., August, 1886, p 
